A reconfigurable optical add/drop multiplexer (ROADM) can remotely implement dynamical switching of an add/drop optical wavelength of a service optical signal by means of software grooming, so that a fiber connection does not need to be manually changed at a station, thereby significantly reducing operating costs of an entire system. The service optical signal is an optical signal that is transmitted by the ROADM and that carries service information. Currently, the ROADM has been widely applied to key network nodes, and therefore, performance of the ROADM is crucial to reliability and maintainability of an existing network. The ROADM may complete adding/dropping of an optical path on one node, and implement grooming of wavelength-level cross-connections passing through an optical path.
Generally, a currently-used ROADM is implemented by using a wavelength selective switch (WSS). The WSS is an ROADM subsystem technology that develops rapidly in recent years. The WSS features a wide frequency band and low dispersion, supports independence between a port and a wavelength, that is, any output port of the WSS can transmit an optical signal of any wavelength, and supports a higher dimension. A WSS-based ROADM is gradually becoming a first choice for a high-dimension ROADM.
In the prior art, an optical splitter is disposed at an output fiber port of the WSS, and by using the optical splitter, a few optical signals are split from service optical signals that are output from the output fiber port. The split optical signals are input to a detector, so as to monitor performance of the WSS. In this solution, some optical signals can be split only when there are service optical signals that are output from the output fiber port, and the performance of the WSS is monitored by using the split optical signals. When no service optical signal is transmitted at the output fiber port of the WSS, the performance of the WSS cannot be monitored. In the prior art, monitoring the performance of the WSS depends on the service optical signal that is input to the WSS, and consequently, the performance cannot be monitored when no service optical signal is input to the WSS.